Prime Minister Theresa May urged her party Wednesday to back her to deliver bold change for Britain, but her attempt to move past Brexit splits was marred by a protest, a collapsing set and a coughing fit.

The Conservative leader used her closing speech to the party's annual conference to call for national unity after the divisive EU vote, and promise reforms including a major new programme of housebuilding.

But May's address was stopped mid-way when a prankster handed her a P45 -- a form given to those leaving a job -- claiming he had been sent by rebellious Foreign Secretary Boris Johnson.

No sooner had she resumed, than May was overtaken by a prolonged coughing fit, which continued on and off throughout the rest of the speech.

To make matters worse, the slogan on the wall behind her -- "building a country that works for everyone" -- began to collapse, with two letters falling off.

It was a farcical end to a four-day conference in the northwestern city of Manchester which has been marked by a subdued mood, a lack of big policies and lukewarm support for May herself.

"It just couldn't get worse than this. What a disaster. It's a shambles, not a government," tweeted Seema Malhotra, a lawmaker with the opposition Labour party.

But May's distress appeared to rouse the delegates, who gave her repeated standing ovations -- and when she could not speak, urged her on by shouting "Come on, prime minister!"

"Obviously she was having difficulties, but what we saw was her tenacity," Stephen Kerr, a Scottish member of parliament, told AFP.

"She's been through so much in the past few months, but she carries on and that's why we’re behind the prime minister."

- 'I am sorry' -
This year's conference has been overshadowed by Johnson's decision to set out his rival vision for Brexit in a newspaper article last month.

The move by a politician known for his leadership ambitions was viewed as an attempt to goad the prime minister, and many saw her failure to sack him as a proof of her weakness.

Four months after the June election, which was called by May but which saw her lose her parliamentary majority, she began Wednesday's speech with an apology.

"I hold my hands up for that. I take responsibility," she said. "And I am sorry."

But she warned her ministers, who sat in front of her, that it was time to "shape up and give the country the government it needs".

"Working people up and down this land... must be our only focus," she said.

As she spoke, Johnson was embroiled in another row, this time over Libya, following comments he made at a fringe event on Tuesday evening.

He said the conflict-torn country could become a magnet for tourists and investors if it can "clear the dead bodies away" first.

- No deal on Brexit? -
After her tired appearance this week forced her to deny she was "miserable", May said she was driven by a desire to "root out injustice and give everyone in our country a voice".

She promised to fight to ensure "that each new generation should be able to build a better future".

May announced a £2 billion (2.25 billion euros/$2.65 billion) investment in housing, promising to dedicate her premiership to tackling the shortage of affordable homes.

She also promised to fulfil a manifesto pledge to put a price cap on energy bills.

May had little to say on Brexit, even as the negotiations with Brussels reach a crucial point in the next few weeks.

She set out her main principles in a major speech in Florence last month, but the issue continues to divide her party.

But she left open the prospect of walking away without a deal -- a threat backed by rightwing Tories who have been drawing large crowds to fringe meetings this week.

"I believe it is profoundly in all our interests for the negotiations to succeed but... it is our responsibility as a government to prepare for every eventuality," she said.